[RFC] Migrating to ESLint, and code formatting with Prettier

## Summary

We need to ensure our development tooling keeps in track with the current practices. [TSLint is already deprecated](https://medium.com/palantir/tslint-in-2019-1a144c2317a9). Therefore, we will need to port the configs for our [development standard](https://github.com/kata-ai/development-standard) to its ESLint counterpart.

Moreover, to prevent the headache of formatting code, we should standardise using [Prettier](https://prettier.io/), which is supported on many editors, and is runnable during commit time with tools like [lint-staged](https://github.com/okonet/lint-staged).

## Motivation

This RFC serves as a baseline for proper linting + formatting within all JavaScript/TypeScript codebase within Kata.ai, to ensure all JavaScript/TypeScript codes align to the Development Standard.

In future RFCs, we may also tinker around with tools like `lint-staged` for automatically running Prettier on commit time.

## Exceptions

For projects within Kata.ai that are about to be sunset, this change need not applied.

## Drawbacks

We need to factor in maintenance costs in applying the new ESLint config. In many cases, most of the code formatting issues can be solved by Prettier implementation. In addition, since the ESLint config as it stands is an extension of Airbnb config, any linting rules that didn't align to our Standard shall be fixed and published to npm.

## Additional context

The new ESLint config has already been developed alongside [Aksara UI](https://github.com/kata-ai/aksara-ui), and we use that project, as well as other frontend projects within Kata.ai, to dogfood the ESLint config's implementation.

The ESLint config will live in https://github.com/kata-ai/eslint-config-kata. Further changes to the ESLint config shall go through another RFC process in the Development Standard.